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After months of hype, Apple has released iOS 5 for current iPhone 3G S and 4 owners, for iPad and iPad 2 owners, and for third- and fourth-generation iPod Touch owners. I survey its key new features in the slideshow "iOS 5 and iCloud: The InfoWorld visual tour," but the fact is that iOS doesn't exist in isolation. It competes with Google's Android OS, and the group of smartphones running Android now significantly outsells the iPhone. (It's a different story in tablets, where the iPad is trouncing everyone, including Android.)

You can see the effects of the healthy competition in one of iOS 5's major new features: Notification Center, clearly based on Android's well-regarded notifications capability that allows users to access alerts and notices from any application. But iOS 5 largely advances the groundbreaking iPad, iPhone, and iPod Touch in its own ways, as well as adapting recent enhancements to Apple's latest desktop OS, Mac OS X 10.7 Lion.

Apple delivers a unified mobile OS for the iPad, iPhone, and iPod Touch, whereas Google has two Android tracks: one for tablets and one for smartphones. Google does plan on unifying the two Android OSes into a single one later this year, in Android 4.0 "Ice Cream Sandwich" now under development, but for now, Android 2.3 "Gingerbread" for smartphones and Android 3.2 "Honeycomb" for tablets are the ones competing with iOS 5.

Note that "Gingerbread" is a fairly minor update to Android 2.2 "Froyo," which most Android smartphones still run. "Gingerbread" adds an improved onscreen keyboard design, the ability to amend auto-correction suggestions when typing, a new universal menu shortcut to the Manage Applications preferences, support for multiple cameras, an updated downloads manager for the browser, and support for near-field communications (NFC) radios. (I tested "Gingerbread" on a Google Nexus One, which doesn't support NFC or have multiple cameras.) Note too that most Android tablets -- including the Samsung Galaxy Tab 10.1 used for this review -- still run Android 3.1, and that the 3.2 update adds very little to the 3.1 version: a zoom mode for better display of smartphone apps and better apps-sizing support for 7-inch tablets.

Without further ado, here's the head-to-head comparison. Click Next Page to continue, or jump directly to any section that interests you.